Fluorescent lamps are well known in the art and are characterized as low pressure arc discharge lamps which include a pair of electrodes sealed in an elongated envelope whose interior surface is coated with phosphor. The envelope contains a quantity of mercury and a rare gas at a reduced pressure, for example, in the order of 1-5 torr.
During lamp manufacture, about 10-40 milligrams of elemental mercury is sealed in each fluorescent lamp. It is known that most of this mercury adheres to the phosphor coating with only a very small portion of the mercury being in the form of mercury vapor. After the alkali earth metal oxides coating the lamp electrodes are volatized, the oxides decompose in the discharge space and the freed oxygen converts some of this elemental mercury to a salt or compound such as mercuric oxide (HgO) which is highly soluble.
There is a growing concern that a waste stream resulting from the disposal of fluorescent lamps may leach excessive amounts of this soluble form of mercury. One method of measuring the amount of soluble mercury which may leach from the waste stream resulting from the disposal of fluorescent lamps is described in the Toxicity Characteristic Leaching Procedure (TCLP) prescribed on pages 26987-26998 of volume 55, number 126 of the Jun. 29, 1990 issue of the Federal Register. According to the procedure, the lamp being tested is pulverized into granules having a surface area per gram of material equal to or greater than 3.1 cm.sup.2 or having a particle size smaller than 1 cm in its narrowest dimension. Following pulverization, the granules are subjected to a sodium acetate buffer solution having a pH of approximately 4.93 and having a weight twenty times the weight of the granules.
At the present time, the Environmental Protection Agency defines a maximum concentration level for mercury at 0.2 milligram leachable mercury per liter extract fluid when the TCLP is applied. According to present standards, a fluorescent lamp is considered non leachable when less than 0.2 milligram per liter of leachable mercury results from a TCLP extraction.
Various methods have been proposed which attempt to treat or process burned-out discharge lamps or scrap lamp exhaust tubing containing mercury in order to reclaim the mercury and thereby reduce the amount of mercury-contaminated scrap glass. For example, U.S. Pat. No. 4,268,306 (Bjorkman) discloses a treatment whereby the expanded or scrapped lamps are crushed into fragments which are then placed in a treatment vessel in which the mercury is recovered by distillation processes. This treatment is carried out batchwise in a sealed container into which nitrogen is introduced. The container is heated and placed under vacuum so as to vaporize the mercury. The vaporized mercury is then removed from the container through a bottom outlet and condensed in a cooling trap. It is apparent that following the process, the treated lamp fragments (i.e., glass and phosphor) may be dumped without concerns about mercury leaching.
U.S. Pat. No. 4,715,838 (Kulander) teaches a method and apparatus for recovering the luminescent material from mercury vapor electric discharge lamps whereby the amount of lamp waste requiring treatment in the distillation chamber can be reduced thereby increasing the capacity of the chamber with respect to the number of lamps. After the ends of the lamp bulb or tube are separated from the intermediate bulb, the luminescent material is loosened from the inner wall surface of the bulb part with the aid of a stripping device which is arranged to be inserted into the bulb part from one end thereof. The loosened material is collected with the aid of a suction device connected to the other end of the bulb part and thereafter may be introduced into the distillation chamber, thereby obviating the need to fill the chamber with the residual "clean" glass bulb.
Japanese Patent Application No. 58-184558 (Kitsugi et. al.) teaches a method for solidifying discarded fluorescent lamps and insolubilizing the mercury contained therein. The method involves adding sulfur to crushed fluorescent lamp waste in the proportion of 0.1-5 parts by weight per 100 parts by weight of the discard. The result is placed into a ball mill and pulverized an amount of time sufficient to produce granules with sizes 5 millimeters or less. Cement and water were added and the result is kneaded. The kneaded material prepared in this way is put into molds so as to form a stabilized solidified material having a mercury concentration of less than 0.005 milligram per liter water.
U.S. Pat. No. 4,435,284 (Heytmeijer) teaches a process for removing residual mercury from scrap fluorescent lamp exhaust tubulation or similar scrap glass. A very small predetermined amount of finely divided silica or alumina powder is added to the mercury contaminated scrap glass and the mixture is agitated for a very short predetermined time during which the mercury is stripped from the tubulation. The separated mercury, powder and glass mixture is then decanted through a screen of suitable mesh to remove the separated mercury and powder from the glass and the mercury is then rinsed with a suitable solvent to remove the oxide powder from the mercury.
While these processes may be effective in separating mercury from lamp fragments or scrap glass or for insolubilizing the mercury contained in discarded fluorescent lamps, each process requires treatment equipment which may be relatively expensive.